Bears know that the apples are ready…

It’s time to pick apples – at least according to the local wildlife. This weekend, we happened upon an adult black bear and her cubs munching on the apples down by the Trego railroad crossing in the wee morning hours.

Bears aren’t too picky about ripeness. Like many mammals, they’re attracted to the smell of fermentation – (the smell indicates a fruit has the highest calorie content it’s going to get). As apples get ripe (and then overripe) they become even better bear attractants.

Can bears become inebriated? Certainly! Glacier Park had a number of incidents back in the 80’s. Several railroad spills released thousands of tons of barley and corn. Buried by cleanup efforts, much of the grain fermented anaerobically, producing high volumes of alcohol. Upon emerging in the spring, bears promptly dug up the fermented mash, wish predictable consequences.

While unattended grain can ferment well, fruit left to its own devices rarely produces enough alcohol to have an effect on large mammals. Bears may be in your apple trees in the near future, but at least you won’t have to worry about them being drunk and disorderly. Not from that, anyway.


Bear Hibernation Part II

While I was working on black bears in the Yaak for my Masters degree, I had the pleasure of cooperating with Dr. Ralph Nelson from the Mayo Clinic in Rochester, Minnesota. Dr. Nelson was studying hibernation in bears for a variety of human-related reasons, not the least of which was to assist NASA with sending man to Mars. The theory was that if we could induce hibernation in people, we could therefore select astronauts that were somewhat rotund and put them to sleep for 6 months while we sent them off through space. Not only would this alleviate long periods of boredom, but it would also greatly reduce the amount of necessary resources such as food and fuel.

Dr. Nelson had several black bears in captivity in Minnesota that he was studying and from which he collected blood and urine samples. He wanted to know if various parameters such as proteins and hormone levels were similar in wild bears. Dr. Nelson and one of his assistants joined me in the Yaak in March of 1988, where we entered the dens of a number of radio-collared bears that I was monitoring. We took snowmobiles to wherever the bears were denning, tranquilized them, and drew blood and urine samples for later analysis. To my knowledge, researchers have yet to identify what exactly triggers hibernation, but they have found a number of things that can be hugely beneficial for people.

For one thing, bears are able to recycle their nitrogenous waste (urea) and reconvert it back into protein, or muscle mass. Bears have microbes in their gut that converts urea into a form of nitrogen they can use to make new amino acids, which are the building blocks of protein. Imagine doing nothing for 5 or 6 months and you still have the same amount of muscle as before!  This has huge implications for patients on dialysis, whose kidneys are failing and must have their blood cleansed (nitrogen removed) by a machine.

Another thing they discovered is that bears do not experience osteoporosis, or weakening of the bones. Again, if you or I were bedridden for a couple of months, our bones would begin to weaken due to a loss of calcium. This is also a problem with space travel where astronauts do not put pressure on their bones due to a lack of gravity. Researchers have discovered that calcium lost from the bones of bears during hibernation is recycled and re-deposited, resulting in no net loss or strength!

In order for bears to successfully hibernate and reproduce, they must put on very large stores of fat, which are then lost. This process is repeated yearly. Obese people with excess fat often exhibit problems with diabetes and heart disease. Again, bears exhibit no such issues. For patients exhibiting problems with gall stones, scientists have isolated a compound called Ursodiol, which is found in bear bile and is produced by the gall bladder. This compound has since been reproduced synthetically and is currently used by doctors to dissolve cholesterol-laden gall stones and to treat certain liver diseases.

As time goes on, it is likely even more fascinating aspects of bear physiology will be discovered. It will be interesting to see what’s next!


Bear Hibernation (Part I)

People are fascinated by bears for a variety of reasons, not the least of which is their ability to hibernate. Imagine an animal much like people in many ways, being able to crawl into a den for 5-6 months and remain there, without eating, drinking, urinating or defecating, the entire time. As if that wasn’t enough, females give birth to their young in January and nurse and care for them until they eventually leave the den in April or May.

I began working on bears in 1976 in the North Fork of the Flathead under the guidance of Dr. Charles Jonkel and the Border Grizzly Project. In the 1980’s, I did my Master’s Degree on the effects of hunting on black bears in the Yaak. Part of my research involved entering the dens of hibernating black bears, tranquilizing them, and replacing their aging radio collars with fresh ones and gathering biological data. It was an aspect of my life I will never forget.

For starters, when it comes to hibernation, it is important to first understand bear reproduction. Bears exhibit an interesting reproductive strategy called “delayed implantation”. Breeding occurs from late May to early July. The fertilized eggs of a female will cleave several times and form a blastocyst, but unlike most other mammals, the blastocyst remains free-floating rather than implanting in the wall of the uterus and developing further. The blastocysts remain free-floating until the female bear enters the den in the fall, usually late September or early October. At that time, the female bear’s body somehow senses if she has acquired sufficient fat reserves to not only sustain the mother for 6 months, but also allow the young to develop and then nurse them after they are born. If it has been a good year with lots of berries and the female has acquired a thick layer of fat, the blastocysts will then implant in the uterus and development begins. On the other hand, if it has been a poor berry year and an insufficient amount of fat has been accrued to produce and nurse her young while in the den, the blastocysts are simply resorbed by the female or expelled. This unique reproductive mechanism saves the female from wasting a lot of energy needlessly that might also jeopardize her life.

Hibernation itself is a physiological term that involves much more than just sleeping. Breathing and heart rates slow considerably and body temperatures drop 10-12 degrees F. In “true” hibernators like chipmunks and ground squirrels, heart rates may drop to only a few beats per minute and body temperatures may approach freezing. They are very stiff and comatose and unable to defend themselves, if necessary. Also, they must arouse periodically to urinate and defecate. Because the heart rates and body temperatures of bears drop only moderately, many biologists assert that bears are not true hibernators. However, because they can give birth in the den and defend themselves if necessary, all without eating and drinking for 5-6 months, other biologists refer to them as the “ultimate” hibernator!

-Tim Thier